The measurement of fluid flow velocities and hence volumetric flow in a fluid conveyance has often been a perplexing problem. The primary source of difficulty is that many measurement procedures disturb the fluid flow profile so that an accurate measurement of the "original" or undisturbed fluid flow cannot be made. Other methods, which probably do not disturb the fluid flow profile (for example Wyler, U.S. Pat. No. 3,940,985, issued Mar. 2, 1976, and Malone et al, U.S. Pat. No. 3,564,912, issued Feb. 23, 1971), are based upon arbitrarily selected, substantially inflexible, approximations and analytical techniques which may unknowingly, under some circumstances, provide somewhat inaccurate measurements which would be unacceptable in commercial practice.
The principal applications for measuring fluid flow rate are oil and gas flows through pipelines extending between supplier and customer, industrial applications where an accurate determination of fluid flow rate is necessary, and in some experimental laboratory situations in which an accurate measurement of flow is important. In each of these applications, errors on the order of 1% may be unacceptable.
The principal object of this invention is therefore an accurate flow rate determining apparatus and method which is accurate under substantially all operating conditions. Other objects of the invention are an apparatus and method having high reliability, substantially low instrumentation costs, a large degree of flexibility in the placement of the measurement equipment, and providing a consistent and repeatable measurement based upon the physical parameters of the fluid flow system.